1. Technical Field of the Invention
This invention generally relates to injection blow molding machines and, more particularly, to a method for controlling the distribution of material in products formed by injection blow molding machines.
2. Discussion
A traditional injection blow molding machine has several stations. These stations include an injection molding station, a conditioning station, a blow molding station, and a take out station. A rotating mechanism or table transfers the plastic product to and through the various stations of the injection blow molding machine. Product formation, however, begins in the injection molding station where a plastic parison is formed.
In the injection molding station, a cavity mold is brought into contact with a neck mold. Then, a core rod assembly is inserted into the cavity mold through the neck mold. Next, an injection nozzle is brought into contact with the cavity mold and molten resin is then forced into the cavity defined by the cavity molds, thereby forming a parison. After the parison has been formed, the neck mold and the core rod assembly are moved away from the injection molding station. The parison is still contained within the neck mold and the rotating mechanism then rotates the neck mold to the next station.
In the conditioning station, the rotating mechanism positions the neck mold containing the parison above one or more heating cylinders. Then, one or more heating cores are inserted through the neck mold into the parison as heating cylinders are elevated to thereby surround the parison. The parison is then heated to a predetermined temperature. After conditioning, the heating cores and the heating cylinders are removed from the station. The rotating mechanism then rotates the parison to the next station.
In the blow molding station, blow molds are closed around the parison. Next, a blow core assembly engages the neck mold and a stretch rod is inserted into the parison thereby stretching the parison in an axial direction. In a synchronized movement, the parison is supplied with blown air so that the parison expands within the blow mold to form a hollow molded container. After the container is formed, the blow molds and the blowing core assembly are moved away from the station and the rotating mechanism rotates the neck mold carrying the molded plastic container to the next station.
In the take out station, the molded container is removed from the neck mold in a conventional manner such as expanding neck mold halves to release the container and/or through other means. After the molded container has been removed, the rotating mechanism then rotates the neck mold to the cavity molding stage where the process is repeated.
Proper material distribution is critical throughout this process. The quality of the molded container and its ability to retain a product placed within it depends on a proper distribution of the plastic forming the parison as it is transformed into the molded container. Therefore, a need exists to be able to control the distribution of material throughout the injection blow molding process.
Additionally, a need exists for controlling material distribution without having to significantly modify existing machine tooling.
In accordance with a preferred embodiment of the present invention, a core rod positioning device and method is provided. The core rod positioning device and method permits material distribution in the resultant container to be manipulated or fine tuned. This is achieved by slightly altering the conditioning of the preforms, the alteration being specific for each container mold cavity.
The core rod positioning device comprises a sleeve having an outer surface that defines the interior surface of the preform being molded using that core rod assembly. Within the sleeve is a mandrel. Portions of the mandrel define a first passageway therethrough and which terminates at a port located in the exterior surface of the mandrel. The exterior surface of the mandrel also cooperates with an interior surface of the sleeve thereby defining a second passageway located between the sleeve and the mandrel. Additionally, an adjustment mechanism is operably coupled to the mandrel allowing the port of the mandrel to be adjusted relative to the sleeve.
About the sleeve is located a cavity mold. Between the two, the preform is formed. As the preform is formed it is possible for the material of the preform to be unevenly cooled. As a result, during blow molding, the preform may stretch unevenly thereby resulting in a poor or unacceptable container.
A fluid coolant is circulated through the first and then the second passageway of the mandrel to control the temperature of the material between the sleeve and the cavity mold. When the mandrel is centered within the sleeve, generally even cooling is affected on the preform. If the mandrel is shifted relative to the sleeve, additional cooling can be directed to specific areas of the preform. As a result, material distribution can be controlled by positioning the mandrel port thereby cooling a specific portion of the preform and affecting how the preform stretches in the blow molding station.
As evident from the above, with the core rod positioning device being located within the core rod assembly, there is no need to significantly modify the other existing machine tooling.